Help needed - Loading new Rom

Having successfully rooted the phone, I did the following; 1. Copy your custom ROM "zip" file to your SD card (Root directory).2. Turn off your phone.3. Turn on your phone by holding the power button and the volume down button together.4. Once you see the white screen, choose "Recovery"5. Make a full wipe/format and clear all cache. 6. Choose "install from sdcard/zip file" and then choose your Custom ROM zip file from your SD card to flash your Custom ROM.The following then comes up; Clockworkmod recovery V5.0.2.0Installing/SDCard/RUU_Saga_H3G_UK_1.31.771.1_Radio_20.28b.30.0805U_38.03.02.14_M_release_178937_signed.zipFinding update package ...Opening update package ...Installing update ...Installation aborted.Therefore, I cannot install this new Rom. Does anyone know what I'm doing wrong.Thanks,